Phonographic reproducer.



PGNGGRPHKC REPBODUGEE.

Leed.

Speccation of ietters Patent.

Patented Sept. i8, i917.

Application led August 30, l. Seria1No.-7,990.

ing the use of a suitable case having a soundwave exit foreonnection with an amplifier, recombination with a diaphragm supported at its 4marginal edges within the case acrossy the exit and ea vibrator' connected to the'diaphragm and provided with a styius for contact with the sound-producing record.

It is well known that in instruments of this character the reproduction ot I-sounds, and'particuiarly the more refined or classic musical renditions, both Vocal and instru.

' mental, is accompanied by more or less discordant or interferent tones which is believed to be caused by sympathetic vibrations of the conning mediums for the diaphragm and air columns of said reproducer.

This theory so far as it reiates to the pro duction orn interferent vibrations is probably correct, but so far as i am aware does not deal with the quality of those vibrations or the-manner in which they affect the rythmic motion of the sound-waves as produced by the Ivibration of the diaphragm.

in extending my investigations along this line, ind that the diaphragm case'usuaiiy employed is constructed of highly vibratory metal, such as steei or equivalent material, which, owing to its excess magnitude and rigidity as compared with the size and rin gidity of the diaphragm, must necessarily Iproduce sympathetic vibrations ot proportionately higher frequencies, thus producinga corresponding agitation oi' the air in and around the rhythmic vibrations produced by the diaphragm, andcausing the accompanying shriii tones commonly -oh-y served in instruments oifthis character.

My investigation shows that these interierent high frequency vibrations'are produced more pronouncediy by the back of the diaphragm case between the hub and rim which incidentally creates a corresponding agitation of the intervenin air coiumn between the back of the case an diaphragm,

and causes vibrations of similar frequency4 to be set up in the more rigid parts of the diaphragm nearest its point of securement around lts marginal edges which would tend to produce nodal points in the diaphragm whereby different parts thereof would be vihrated at different frequencies, the cen. trai portion tending to vibrate rhythmically vin accordance with the soundwaves of the record as 'produced by the contact 'of the stylus therewiti, while the portions near the'marginal edges oi' the diaphragm ap' parently vibrate at a much higher frequency.

The main object, therefore, of my present invention is to reduce to a minimum he production or transmission of interferent vibrations from the diaphragm case .to the diaphragm, or from said case to the exit for the sound-waves produced by the diaphragm.

in other words, have sought to provide economical means capable of being piaced in any of the standard forms of reproducers, for eliminating or deadeningthe shrillness` or discordant tones commonly presentan instruments of this character.

Other objects and uses relating to specific parts oi the device will be brought out in the foilowing description.

in the drawingse Figure i is a front face View of a phonographic reproducer embodying my invention.

Fig. 2 is an eniarged sectional view of the same device, taken on line 2-2, Fig. 1.

f3 and e are perspective views of the detached inner and outer disks upon which my invention is based.

in order that my invention may be clearly understood, i have shown an ordinaryI Columbia reproducer comprising a case -1- having a hoilowhub -2 and a rim -3 for receiving a diaphragm 4- which is held in piace around its marginal. edges'by cushion rings -5-- and a screw ring -6-, the diaphragm having the centrallportion attached in the usual manner `to one end of thelever m7-, the other end .of which is adapted to carry the stylus -8-, shown by dotted linesin Fig. 1.

@ne or the features of my invention consists in providing a circular concavo-convex disk -9- of substantially the same diameteryas the diaphragm -4- and having itsmarginai edges clamped between the inner that its remaining portions be interposed between the diaphragm and back of -the case in spaced relation thereto with the convex Aside facing the diaphragm, and therefore? the concave side facing the usual soundwave exit H10- centrally in the back of the case. g Tl'iisdisk -9- is provided with a central opening ,-111- co-axial with, but slightly larger than the exit. -l0-, so as to allow free passage ofthe soundivaves produced by the vibration of 'the diap ragni.

. By locating the disk -9 in the manner described, it divides the chamber between the diaphragm and back of 'the caso into relatively shallow compartments -12- and -15. This disk 5L- more nearly rthe thickness of the diaphragm than the back of the case, and While acts as a baiiie to prevent the transmission of the nigh frequency vibrations from the case 1M to .the diaphragm, it preferably made of thin Copper, lead or equivalent material which is incapable of rhythn'iic iibrations, partienlarly of high frequency and, therefore, tends to negative'any high frequency agitation of the air which might be. produced hv the sympathetic vibration of the case -1- as the diaphragm is vibrated in the usual man ner for reproducing sounds. For a simi inner face of disk e ne tubuh l tend fitting elo 1 case for the p tralizing fectsI which may be produced by the vibration of the ad) gint portions of the case 1f-n The arop uhe diaphragm mi and by making the central opening M11- of additionally neu i. v w v Jl or deaoeinng sound-i e eirde of the. central portion of pared vvith the enit opening in the case, allows both disks --9 and --1lto be used in the standard forms of reproducers without any change or reconstruction of the parts thereof, the marginal edges of both disks being clamped in place by the saine means which holds the diaphragm.

Another object in making the opening -11- in the disk -9- relatively larger than the exit opening in the case is to permit greater freedom of movement of the soundwaves to the exit as produced by the maximum degree of vibration of the central portion of the diaphragm.

The chamber -13-, while' shallow, affords ample clearance for the'vibration of the disk 4) or course greatest the diaphragm without contact With the disk and inasmuch as the degree of amplitude of the diaphragm is greatest at the center and diminished toward the edges, it follows thatY the rhythmic vibration ofthe air insaid chamber is greatest at the center, or within the area of the opening 11- in vhicb., by reason of its proximity, serves to concentrate the sound-Waves more closely within the area of the exit tube -l5.

The purposes, therefore, of interposing the non-vibrant disks -9- and 111- between the diaphragm and back of the case are First. To prevent `the transmission of sound-Waves from the diaphragm to' the hack of the case and vice versa.

Second. To prevent the commingling of any sound-waves which may be produced by sympathetic vibration of the .diaphragm case into the exit leading to the amplifier, and i Third. To increase the fullness or quality of the tones produced by the diaphragm so that they will correspond more closely to the original tones as represented by the sound-producing record.

lli/ hat l claim is: y

1. in a phonographic reproducer, a nonvibrant concave-convex disk between the.

diaphragm and back of the case, and prof' vided with an opening registering with the sound-Wave exit in the case, said disk having its concave side facing the exit.

ln a phonographic reproducer, a lining disk of non-vibrant materiaL lying against the inner face of the back of the case, and provided with a tubular hub of the same material fitted within and extending through the sound-wave exit in said case.

3. 1n a phonographic reproducer, a lining disl' of non-vibrant material lying against the inner face of the back of the case and provided with a tubular hub of the same material fitted Within and extending through the sound-wave exit in said case, and a concavo-convex disk of non-vibrant material interposed between the diaphragm and said lining disk and provided With a central opening co-axial with and relatively larger than that in the tubular hub, said concavoconvex disk having its concave side facing the lining disk.

In witness whereof I have hereunto set my hand this 21st day of August, 1915.

EDWARD G. SMlTH. lVitnesses:

H. E. CHASE, ALICE M. CANNON. 

